Network Working Group W. Kumari
Internet-Draft Google
Intended status: Standards Track E. Hunt
Expires: June 23, 2019 ISC
R. Arends
ICANN
W. Hardaker
USC/ISI
D. Lawrence
Oracle + Dyn
December 20, 2018
Extended DNS Errors
draft-ietf-dnsop-extended-error-03
Abstract
This document defines an extensible method to return additional
information about the cause of DNS errors. Though created primarily
to extend SERVFAIL to provide additional information about the cause
of DNS and DNSSEC failures, the Extended DNS Errors option defined in
this document allows all response types to contain extended error
information.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 23, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Extended Error EDNS0 option format . . . . . . . . . . . . . 3
3. Use of the Extended DNS Error option . . . . . . . . . . . . 4
3.1. The R (Retry) flag . . . . . . . . . . . . . . . . . . . 5
3.2. The RESPONSE-CODE field . . . . . . . . . . . . . . . . . 5
3.3. The INFO-CODE field . . . . . . . . . . . . . . . . . . . 5
3.4. The EXTRA-TEXT field . . . . . . . . . . . . . . . . . . 5
4. Defined Extended DNS Errors . . . . . . . . . . . . . . . . . 5
4.1. INFO-CODEs for use with RESPONSE-CODE: SERVFAIL(2) . . . 6
4.1.1. SERVFAIL Extended DNS Error Code 1 - DNSSEC Bogus . . 6
4.1.2. SERVFAIL Extended DNS Error Code 2 - DNSSEC
Indeterminate . . . . . . . . . . . . . . . . . . . . 6
4.1.3. SERVFAIL Extended DNS Error Code 3 - Signature
Expired . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.4. SERVFAIL Extended DNS Error Code 4 - Signature Not
Yet Valid . . . . . . . . . . . . . . . . . . . . . . 6
4.1.5. SERVFAIL Extended DNS Error Code 5 - Unsupported
DNSKEY Algorithm . . . . . . . . . . . . . . . . . . 6
4.1.6. SERVFAIL Extended DNS Error Code 6 - Unsupported
DS Algorithm . . . . . . . . . . . . . . . . . . . . 6
4.1.7. SERVFAIL Extended DNS Error Code 7 - DNSKEY missing . 6
4.1.8. SERVFAIL Extended DNS Error Code 8 - RRSIGs missing . 7
4.1.9. SERVFAIL Extended DNS Error Code 9 - No Zone Key Bit
Set . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. INFO-CODEs for use with RESPONSE-CODE: REFUSED(5) . . . . 7
4.2.1. REFUSED Extended DNS Error Code 1 - Lame . . . . . . 7
4.2.2. REFUSED Extended DNS Error Code 2 - Prohibited . . . 7
4.3. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3) . . . 7
4.3.1. NXDOMAIN Extended DNS Error Code 1 - Blocked . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. new Extended Error Code EDNS Option . . . . . . . . . . . 7
5.2. New Extended Error Code EDNS Option . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
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8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction and background
There are many reasons that a DNS query may fail, some of them
transient, some permanent; some can be resolved by querying another
server, some are likely best handled by stopping resolution.
Unfortunately, the error signals that a DNS server can return are
very limited, and are not very expressive. This means that
applications and resolvers often have to "guess" at what the issue is
- e.g. was the answer marked REFUSED because of a lame delegation, or
because the nameserver is still starting up and loading zones? Is a
SERVFAIL a DNSSEC validation issue, or is the nameserver experiencing
a bad hair day?
A good example of issues that would benefit by additional error
information are errors caused by DNSSEC validation issues. When a
stub resolver queries a DNSSEC bogus name (using a validating
resolver), the stub resolver receives only a SERVFAIL in response.
Unfortunately, SERVFAIL is used to signal many sorts of DNS errors,
and so the stub resolver simply asks the next configured DNS
resolver. The result of trying the next resolver is one of two
outcomes: either the next resolver also validates, a SERVFAIL is
returned again, and the user gets an (largely) incomprehensible error
message; or the next resolver is not a validating resolver, and the
user is returned a potentially harmful result.
This document specifies a mechanism to extend (or annotate) DNS
errors to provide additional information about the cause of the
error. When properly authenticated, this information can be used by
the resolver to make a decision regarding whether or not to retry or
it can be used or by technical users attempting to debug issues.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Extended Error EDNS0 option format
This draft uses an EDNS0 ([RFC2671]) option to include Extended DNS
Error (EDE) information in DNS messages. The option is structured as
follows:
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1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | R | RESERVED |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | RESPONSE-CODE | INFO-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
8: | EXTRA-TEXT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Field definition details:
o OPTION-CODE, 2 octets (defined in [RFC6891]), for EDE is TBD.
[RFC Editor: change TBD to the proper code once assigned by IANA.]
o OPTION-LENGTH, 2 octets ((defined in [RFC6891]) contains the
length of the payload (everything after OPTION-LENGTH) in octets
and should be 4 plus the length of the EXTRA-TEXT section (which
may be a zero-length string).
o The RETRY flag, 1 bit; the RETRY bit (R) indicates a flag defined
for use in this specification.
o The RESERVED bits, 15 bits: these bits are reserved for future
use, potentially as additional flags. The RESERVED bits MUST be
set to 0 by the sender and SHOULD be ignored by the receiver.
o RESPONSE-CODE, 4 bits.
o INFO-CODE, 12-bits.
o EXTRA-TEXT, a variable length, ASCII encoded, text field that may
hold additional textual information.
3. Use of the Extended DNS Error option
The Extended DNS Error (EDE) is an EDNS option. It can be included
in any response (SERVFAIL, NXDOMAIN, REFUSED, etc) to a query that
includes an EDNS option. This document includes a set of initial
codepoints (and requests to the IANA to add them to the registry),
but is extensible via the IANA registry to allow additional error and
information codes to be defined in the future.
The fields of the Extended DNS Error option are defined further in
the following sub-sections.
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3.1. The R (Retry) flag
The R (Retry) flag provides a hint as to what the receiver may want
to do with this annotated error. Specifically, the R (or Retry) flag
provides a hint to the receiver that it should retry the query to
another server. If the R bit is set (1), the sender believes that
retrying the query may provide a successful answer next time; if the
R bit is clear (0), the sender believes that the resolver should not
ask another server.
The mechanism is specifically designed to be extensible, and so
implementations may receive EDE codes that it does not understand.
The R flag allows implementations to make a decision as to what to do
if it receives a response with an unknown code - retry or drop the
query. Note that this flag is only a suggestion. Unless a
protective transport mechanism (like TSIG [RFC2845] or TLS [RFC8094])
is used, the bit's value could have have been altered by a person-in-
the-middle. Receivers can choose to ignore this hint. See the
security considerations for additional considerations.
3.2. The RESPONSE-CODE field
This 4-bit value SHOULD be a copy of the RCODE from the primary DNS
packet. Multiple EDNS0/EDE records may be included in the response.
When including multiple EDNS0/EDE records in a response in order to
provide additional error information, other RESPONSE-CODEs MAY use a
different RCODE.
3.3. The INFO-CODE field
This 12-bit value provides the additional context for the RESPONSE-
CODE value. This combination of the RESPONSE-CODE and the INFO-CODE
serve as a joint-index into the IANA "Extended DNS Errors" registry.
3.4. The EXTRA-TEXT field
The ASCII-encoded, EXTRA-TEXT field may be zero-length, or may hold
additional information useful to network operators.
4. Defined Extended DNS Errors
This document defines some initial EDE codes. The mechanism is
intended to be extensible, and additional code-points can be
registered in the "Extended DNS Errors" registry. This document
provides suggestions for the R flag, but the originating server may
ignore these recommendations if it knows better.
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The RESPONSE-CODE and the INFO-CODE from the EDE EDNS option is used
to serve as a double index into the "Extended DNS Error codes" IANA
registry, the initial values for which are defined in the following
sub-sections.
4.1. INFO-CODEs for use with RESPONSE-CODE: SERVFAIL(2)
4.1.1. SERVFAIL Extended DNS Error Code 1 - DNSSEC Bogus
The resolver attempted to perform DNSSEC validation, but validation
ended in the Bogus state. The R flag should not be set.
4.1.2. SERVFAIL Extended DNS Error Code 2 - DNSSEC Indeterminate
The resolver attempted to perform DNSSEC validation, but validation
ended in the Indeterminate state. The R flag should not be set.
4.1.3. SERVFAIL Extended DNS Error Code 3 - Signature Expired
The resolver attempted to perform DNSSEC validation, but the
signature was expired. The R flag should not be set.
4.1.4. SERVFAIL Extended DNS Error Code 4 - Signature Not Yet Valid
The resolver attempted to perform DNSSEC validation, but the
signatures received were not yet valid. The R flag should not be
set.
4.1.5. SERVFAIL Extended DNS Error Code 5 - Unsupported DNSKEY
Algorithm
The resolver attempted to perform DNSSEC validation, but a DNSKEY
RRSET contained only unknown algorithms. The R flag should be set.
4.1.6. SERVFAIL Extended DNS Error Code 6 - Unsupported DS Algorithm
The resolver attempted to perform DNSSEC validation, but a DS RRSET
contained only unknown algorithms. The R flag should be set.
4.1.7. SERVFAIL Extended DNS Error Code 7 - DNSKEY missing
A DS record existed at a parent, but no DNSKEY record could be found
for the child. The R flag should not be set.
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4.1.8. SERVFAIL Extended DNS Error Code 8 - RRSIGs missing
The resolver attempted to perform DNSSEC validation, but no RRSIGs
could be found for at least one RRset where RRSIGs were expected.
4.1.9. SERVFAIL Extended DNS Error Code 9 - No Zone Key Bit Set
The resolver attempted to perform DNSSEC validation, but no Zone Key
Bit was set in a DNSKEY.
4.2. INFO-CODEs for use with RESPONSE-CODE: REFUSED(5)
4.2.1. REFUSED Extended DNS Error Code 1 - Lame
An authoritative resolver that receives a query (with the RD bit
clear) for a domain for which it is not authoritative SHOULD include
this EDE code in the REFUSED response. Implementations should set
the R flag in this case (another nameserver might not be lame).
4.2.2. REFUSED Extended DNS Error Code 2 - Prohibited
An authoritative or recursive resolver that receives a query from an
"unauthorized" client can annotate its REFUSED message with this
code. Examples of "unauthorized" clients are recursive queries from
IP addresses outside the network, blacklisted IP addresses, local
policy, etc.
Implementations SHOULD allow operators to define what to set the R
flag to in this case.
4.3. INFO-CODEs for use with RESPONSE-CODE: NXDOMAIN(3)
4.3.1. NXDOMAIN Extended DNS Error Code 1 - Blocked
The resolver attempted to perfom a DNS query but the domain is
blacklisted due to a security policy. The R flag should not be set.
5. IANA Considerations
5.1. new Extended Error Code EDNS Option
This document defines a new EDNS(0) option, entitled "Extended DNS
Error", assigned a value of TBD1 from the "DNS EDNS0 Option Codes
(OPT)" registry [to be removed upon publication:
[http://www.iana.org/assignments/dns-parameters/dns-
parameters.xhtml#dns-parameters-11]
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Value Name Status Reference
----- ---------------- ------ ------------------
TBD Extended DNS Error TBD [ This document ]
5.2. New Extended Error Code EDNS Option
This document defines a new double-index IANA registry table, where
the first index value is the RCODE value and the second index value
is the INFO-CODE from the Extended DNS Error EDNS option defined in
this document. The IANA is requested to create and maintain this
"Extended DNS Error codes" registry. The codepoint space for each
INFO-CODE index is to be broken into 3 ranges:
o 0 - 3583: Specification required.
o 3584 - 3839: First Come First Served.
o 3840 - 4095: Experimental / Private use
A starting set of entries, based on the contents of this document, is
as follows:
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 1
Purpose: DNSSEC Bogus
Reference: Section 4.1.1
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 2
Purpose: DNSSEC Indeterminate
Reference: Section 4.1.2
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 3
Purpose: Signature Expired
Reference: Section 4.1.3
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 4
Purpose: Signature Not Yet Valid
Reference: Section 4.1.4
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 5
Purpose: Unsupported DNSKEY
Reference: Section 4.1.5
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 6
Purpose: Unsupported DS Algorithm
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Reference: Section 4.1.6
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 7
Purpose: DNSKEY missing
Reference: Section 4.1.7
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 8
Purpose: RRSIGs missing
Reference: Section 4.1.8
RESPONSE-CODE: 2 (SERVFAIL)
INFO-CODE: 9
Purpose: No Zone Key Bit Set
Reference: Section 4.1.9
RESPONSE-CODE: 3 (NXDOMAIN)
INFO-CODE: 1
Purpose: Blocked
Reference: Section 4.3.1
RESPONSE-CODE: 5 (REFUSED)
INFO-CODE: 1
Purpose: Lame
Reference: Section 4.2.1
RESPONSE-CODE: 5 (REFUSED)
INFO-CODE: 2
Purpose: Prohibited
Reference: Section 4.2.2
6. Security Considerations
Though DNSSEC continues to be deployed, unfortunately a significant
number of clients (~11% according to [GeoffValidation]) that receive
a SERVFAIL from a validating resolver because of a DNSSEC validaion
issue will simply ask the next (potentially non-validating) resolver
in their list, and thus don't get any of the protections which DNSSEC
should provide. This is very similar to a kid asking his mother if
he can have another cookie. When the mother says "No, it will ruin
your dinner!", going off and asking his (more permissive) father and
getting a "Yes, sure, have a cookie!".
This information is unauthenticated information, and an attacker (e.g
MITM or malicious recursive server) could insert an extended error
response into already untrusted data -- ideally clients and resolvers
would not trust any unauthenticated information, but until we live in
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an era where all DNS answers are authenticated via DNSSEC or other
mechanisms, there are some tradeoffs. As an example, an attacker who
is able to insert the DNSSEC Bogus Extended Error into a packet could
instead simply reply with a fictitious address (A or AAAA) record.
The R bit hint and extended error information are informational -
implementations can choose how much to trust this information and
validating resolvers / stubs may choose to put a different weight on
it.
7. Acknowledgements
The authors wish to thank Joe Abley, Mark Andrews, Peter DeVries,
Peter van Dijk, Donald Eastlake, Bob Harold, Evan Hunt, Geoff Huston,
Shane Kerr, Edward Lewis, Carlos M. Martinez, George Michelson, Petr
Spacek, Ondrej Sury, Loganaden Velvindron, and Paul Vixie. They also
vaguely remember discussing this with a number of people over the
years, but have forgotten who all they were -- if you were one of
them, and are not listed, please let us know and we'll acknowledge
you.
I also want to thank the band "Infected Mushroom" for providing a
good background soundtrack (and to see if I can get away with this!)
Another author would like to thank the band "Mushroom Infectors".
This was funny at the time we wrote it, but I cannot remember why...
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
8.2. Informative References
[GeoffValidation]
IANA, "A quick review of DNSSEC Validation in today's
Internet", June 2016, <http://www.potaroo.net/
presentations/2016-06-27-dnssec.pdf>.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
<https://www.rfc-editor.org/info/rfc2845>.
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[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017, <https://www.rfc-
editor.org/info/rfc8094>.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01:
o Address comments from IETF meeting.
o document copying the response code
o mention zero length fields are ok
o clarify lookup procedure
o mention that table isn't done
From -03 to -IETF 00:
o Renamed to draft-ietf-dnsop-extended-error
From -02 to -03:
o Added David Lawrence -- I somehow missed that in last version.
From -00 to -01;
o Fixed up some of the text, minor clarifications.
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Evan Hunt
ISC
950 Charter St
Redwood City, CA 94063
US
Email: each@isc.org
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Roy Arends
ICANN
Email: roy.arends@icann.org
Wes Hardaker
USC/ISI
P.O. Box 382
Davis, CA 95617
US
Email: ietf@hardakers.net
David C Lawrence
Oracle + Dyn
150 Dow St
Manchester, NH 03101
US
Email: tale@dd.org
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